The Applicant has developed a wide range of printers that employ pagewidth printheads instead of traditional scanning printheads. Pagewidth designs increase print speeds as the printhead does not traverse back and forth across the page to deposit a line of an image. The pagewidth printhead simply deposits the ink on the media as it moves past at high speeds. Such printheads have made it possible to perform full colour 1600 dpi printing at speeds in the vicinity of 60 pages per minute, speeds previously unattainable with conventional inkjet printers.
The high print speeds require a large ink supply flow rate. Not only are the flow rates higher but distributing the ink along the entire length of a pagewidth printhead is more complex than feeding ink to a relatively small reciprocating printhead.
Some of the Applicant's printers provide the printhead as a user removable cartridge. This recognizes that individual ink ejection nozzles may fail over time and eventually there are enough dead nozzles to cause artifacts in the printed image. Allowing the user to replace the printhead maintains the print quality without requiring the entire printer to be replaced. It also permits the user to substitute a different printhead for different print jobs. A draft quality printhead can be installed for some low resolution documents printed at high speed, and subsequently removed and replaced with the original high resolution printhead.
A number of the Applicant's printhead cartridges do not have an inbuilt ink supply for the printhead. These printhead cartridges need to be fluidically coupled to the ink supply upon installation. The supply flowrate to the pagewidth printhead is too high for needle valves because of the narrow internal diameter. This requires the coupling conduits to be relatively large and therefore residual ink leaks freely out of the conduits once decoupled from the supply. This is typically not an issue for needle valve couplings because the surface tension at the open end of a small conduit will usually prevent leakage.
In pagewidth printhead cartridges, the leakage problem is exacerbated by the length of the ink flow paths. If the cartridge is held vertically during removal (or even held with one end slightly raised), the residual ink in the cartridge generates hydrostatic pressure at the lower end. This pressure is a strong driver for leakage and as discussed above, the large conduits provide little resistance.
Shut off valves that close upon disengagement of a fluid coupling are known and used in many devices. Unfortunately, these are unsuitable for the specific requirements of a consumable component such as an ink jet cartridge. Firstly, the ink should not contact any metal components. Reaction between the ink and metal can create artifacts in the print. Secondly, coupling the cartridge to the printer involves relatively high tolerances so that installation is fast and simple. The operation of an ink valve has much smaller tolerances to keep ink flow characteristics within specification. Coupling the printer and the cartridge in a way that also actuates the valve should not require the coupling tolerance to be reduced to that of the valve. Finally, the unit cost of consumables needs to be as low as possible. This requires design simplicity and low production costs.